Field of the Invention
This application relates to a display device, and more particularly, to a display device including a panel self refresh feature and a method for controlling a panel self refresh operation thereof.
Discussion of the Related Art
As display devices have become larger in size and higher in resolution, demand has risen for a high-performance interface that transmits signals between a video source and a display device. To cope with this demand, Vx1 is becoming a substitute for a TV, and a display port (DP) is becoming a substitute for a laptop in the case of IT products.
A display port (DP) interface is an interface regulated by Video Electronics Standards Association (VESA) and is an interface scheme which integrates LVDS (Low Voltage Differential Signaling), the existing internal interface standard, with DVI (Digital Visual Interface), an external connection standard. The DP interface can make not only a digital internal connection between chips, but also a digital external connection between products. As the two divided interfaces are integrated, higher color depth and resolution can be supported by widening data bandwidth. The DP interface has a bandwidth of up to 10.8 Gbps, which is twice or more than that of the existing DVI (maximum 4.95 Gbps), and can simultaneously transmit up to six streams of 1080i (three streams of 1080p) through one connector connection by supporting multi-streams using a micro-packet architecture.
Recently, VESA announced a new version of the embedded display port (eDP). eDP is a companion standard to the DP interface designed for embedded display applications, including notebook PCs, tablets, netbooks and all-in-one desktop PCs. eDP v1.3 includes a new panel self-refresh (PSR) technology that was developed to save system power and further extend battery life in portable PC systems. The PSR technology uses a memory mounted in a display to display an original image as it is while minimizing power consumption, thereby increasing battery usage time in portable PC systems.
FIG. 1 is an overview of the PSR technology included in edP v1.3.
As illustrated in FIG. 1, a display device capable of a PSR operation comprises a source unit 10 and a sink unit 20. The source unit 10 indicates a system, and comprises an eDP transmitter 11. The sink unit 20 indicates a panel portion, and comprises a timing controller 23 and a display unit 24. The timing controller 23 comprises an eDP receiver 21 and a remote frame buffer (RFB) 20. The source unit 10 and the synch unit 20 communicate with each other via an eDP interface.
The display device activates the PSR mode when a still image having no change in display is input, and deactivates the PSR mode in the case of video but not still images. When the PSR mode is activated, still image data is transmitted from the eDP transmitter 11 to the eDP receiver 21 and then is stored in the RFB 22. Then, the operating power of the source unit 10 is turned off, and the data store in the RFB 22 is applied to the display unit 24. Until the RFB 22 is updated with new still image data, the operating power of the source unit 10 remains in the OFF state, and the display unit 24 continues to display the data stored in the RFB 22. That is, when the PSR mode is activated, the display automatically remains the same by the data stored in the RFB 22 even when the working power of the source unit 10 is in the OFF state. This leads to reduced power consumption and increased battery usage time without the user's recognition.
Meanwhile, when the PSR mode is deactivated, data to be transmitted from the eDP transmitter 11 to the eDP receiver 21 is applied to the display unit 24 without being stored in the RFB 22, and the operating power of the source unit 10 continues to remain in the ON state. When the PSR mode is deactivated, power consumption is not reduced.
To perform the PSR mode, the RFB 22 needs to be mounted in the sink unit 20, as mentioned above. The RFB 22 is a component that should be added for the PSR mode, and hence causes a rise in manufacturing costs. Moreover, the PSR mode requires the system power to be turned on/off without the user's recognition (i.e., while the display remains the same). Thus, the original image data should not be lost when stored in the RFB 22. The size of the RFB 22 should be large enough to avoid loss of the original image. However, the use of a large-size RFB 22 will bring about a rise in manufacturing costs and makes it difficult to incorporate the RFB 22 in the sink unit 20, i.e., the timing controller 23.
A variety of lossless data compression methods can be taken into account as an alternative for reducing the size of the RFB 22 and preventing loss of an original image. Still, there has been no method capable of lossless compression of all images that are input within a limited hardware capacity.